This invention relates generally to laminated structural material and in particular to composite structural sheets having flexural vibration dampening properties.
Structural devices having multi-layer arrangements with vibration dampening properties or functions are well known in the art, as exemplified by the disclosures in U.S. Pat. Nos. 4,278,726, 4,609,960 and 4,790,521 to Wieme, Yamauchi et al. and Ide et al., respectively. According to the Wieme patent, a structural laminate is disclosed having a central rigid core layer sandwiched between visco-elastic layers to provide energy absorbing capability. According to the Ide et al. patent, vibrations are damped between rigid plates by means of an elastic rubber block and a viscous fluid sealed within a cavity formed in the elastic block to resist those of the vibrations causing shear.
The vibration dampening techniques associated with the foregoing prior art are unsuitable for use with relatively thin laminates such as those which rely on the structural composite strength of a stack of rigid material layers. Where a viscous fluid is used to resist shearing vibrations as disclosed in the aforementioned Ide et al. patent for example, the vibration dampening arrangement is necessarily bulky and therefore unsuitable for thin structural sheet arrangements.
It is therefore an important object of the present invention to provide a relatively thin sheet material having flexural vibration dampening properties enabling construction of structural components therefrom with a high ratio of dampening to sheet material volume so as to cope with vibration problems in various critical environments.